Passive micromixers are preferred over active mixers for many microfluidic applications due to their relative ease in integration into complex systems and operational flexibility. They also incur very low cost of manufacturing. However

the degree of mixing is comparatively low in passive mixers than active mixers due to the absence of disturbance in the flow by external forces and the inherent laminar nature of microchannel flows. Various designs of complex channel structures and three-dimensional geometries have been investigated in the past to obtain an efficient mixing in passive mixers. But the studies on mixing enhancement with simple planar geometries of passive mixers have been few and limited. The present work aims to investigate the possibility of mixing enhancement by employing simple planar type designs

such as T-mixer and T-T mixer with cylindrical elements placed in the mixing channel. The mixing performance has been evaluated in the

Reynolds

number range of 6 to 700. Numerical results have shown that T-T mixer with cylindrical elements performed significantly well and obtained very good mixing quality over basic T-mixer for the entire range of

Reynolds

number (6 t

o 700). The device has also shown better mixing as compared to basic T-T mixer and T-mixer with cylindrical elements. A larger pair of vortices formed in the stagnation area due to the presence of a cylindrical element in the junction. Cylindrical elements downstream caused significant enhancement in mixing due to splitting and recombining action. The size of the cylindrical element in the T-T mixer has been optimized to obtain better mixing performance of the device. Remarkable improvement in mixing quality by T-T mixer with cylindrical elements has been obtained at the expense of small rise in pressure drop as compared to other passive designs considered in this study. Therefore

the current design of T-T mixer with cylindrical elements can act as an effective and simple passive mixing device for various micromixing applications.